How does social media help in measuring the return of investment of a company?

With social media being a prominent mode to gain popularity, companies streamline their efforts to build an entire presence through twitter, facebook & other popular social media outlets.
Talking about ROI, it is indispensable to form parameters before measuring the profits for a company.
Hence, business and marketing professionals who embark on the journey of social media should define what they want to achieve from using social media outlets